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bcache: Fix a dumb race 

In the far-too-complicated closure code - closures can have destructors,
for probably dubious reasons; they get run after the closure is no
longer waiting on anything but before dropping the parent ref, intended
just for freeing whatever memory the closure is embedded in.

Trouble is, when remaining goes to 0 and we've got nothing more to run -
we also have to unlock the closure, setting remaining to -1. If there's
a destructor, that unlock isn't doing anything - nobody could be trying
to lock it if we're about to free it - but if the unlock _is needed...
that check for a destructor was racy. Argh.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v3.10
This commit is contained in:
Kent Overstreet 2013-07-10 18:04:21 -07:00
parent 8e51e414a3
commit 6aa8f1a6ca
1 changed files with 4 additions and 2 deletions
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6
drivers/md/bcache/closure.c
View File

@ -66,16 +66,18 @@ static inline void closure_put_after_sub(struct closure *cl, int flags)
} else {
struct closure *parent = cl->parent;
struct closure_waitlist *wait = closure_waitlist(cl);
closure_fn *destructor = cl->fn;
closure_debug_destroy(cl);
smp_mb();
atomic_set(&cl->remaining, -1);
if (wait)
closure_wake_up(wait);
if (cl->fn)
cl->fn(cl);
if (destructor)
destructor(cl);
if (parent)
closure_put(parent);